With the recent increasing demand for small-sized and high-performance electric apparatuses, flexible print wiring boards are employed more frequently under severer conditions, for example, at high temperature and high humidity. Thus, there have been strongly required polyimide/metal laminates and flexible print wiring boards withstanding the environment with high temperature and high humidity. Flexible print wiring boards are obtained by directly laminating a metal such as copper on a polyimide film by, for example, metallizing or plating, or by laminating a metal layer such as a copper foil on a polyimide film via an adhesives to thereby give a polyimide/metal laminate and then patterning the polyimide/metal laminate by etching the metal part. Therefore, it is also required that polyimide/metal laminates also have adequate mechanical and electrical characteristics so as to withstand the environment with high temperature and high humidity.
Among all, it is particularly strongly required that the adhesion of polyimide films should withstand the environment as described above.
Thus, various attempts have been made to improve the adhesion of polyimide films.
For example, U.S. Pat. No. 4,742,099 (corresponding to Japanese Patent No. 1,948,445) discloses a technique of improving the adhesion of a polyimide film by adding an organotitanium compound thereto. However, this technique suffers from problems such as causing serious coloration of the film and damaging the fragility of the film due to the existence of titanium atoms at a high concentration within the film.
On the other hand, U.S. Pat. No. 5,227,224 (corresponding to JP-A-6-73209) discloses a polyimide having improved surface adhesive strength which is coated with a metal salt of Sn, Cu, Zn, Fe, Co, Mn or Pd. In the invention, in contrast thereto, not any metal salt of Sn, Cu, Zn, Fe, Co, Mn or Pd but titanium is employed as a metal.
Further, U.S. Pat. No. 5,130,192 discloses a method wherein a polyimide film obtained by coating a solidified polyamic acid film with a heat-resistant surface treatment agent followed by imidization is metallized. However, no highly heat-resistant treating agent is employed in the invention.
In these conventional techniques, there arise some problems such that the films are seriously colored and become fragile due to the titanium element which exists at a high concentration within the film.
Moreover, use of the surface treatment agent suffers from additional problems such that a highly heat-stable one should be employed.
The inventors have conducted intensive studies to solve the problems encountering in the conventional art as described above by providing polyimide/metal laminates and flexible print wiring boards, multi-layered print wiring boards wherein flexible print wiring boards are laminated, rigid flex wiring boards wherein flexible print wiring boards are laminated on hard print wiring boards, tapes for tape automated bonding (TAB) wherein polyimide/metal laminates are applied to TAB, semiconductor packages such as chips on film (COF) wherein semiconductor devices are packaged directly on print wiring boards and multi chip modules (MCMs), magnetic recording films, solar batteries, coating films for aerospace materials and filmy resistance elements which are excellent in environmental resistance.